Time division carrier multiplex telephone system



J. H. HOMRIGHOUS June 7, 1949.

TIME DIVISION CARRIER MULTIPLEX TELEPHONE SYSTEM Filed July 17, 1944 3 Sheets-Sheet l h h Nu IN VEN TOR.

1949- J. H. HOMRIGHOUS 5 TIME DIVISION CARRIER MULTIPLEX TELEPHONE SYSTEM Filed July 17, 1944 3"Sheets-Sheet 2 N\ n l= m m INVENTORJ J. IV-IOMRIGHOUS 2,472,705

TIME DIVISION CARRIER MULTIPLEX TELEPHONE SYSTEM 3 Sheets-Sheet 5 June 7; 1949.

Filed July 1'7, 1944 g: 2- INVENTORL Patented June 7, 1949 TIME DIVISION CARRIER IVIULTIPLEX TELEPHONE SYSTEM John H. Homrighous, Oak Park, 11].

Application July 17, 1944, Serial No. 545,206

14 Claims. 1

This invention relates to an improved multiplex communication system and more particularly to a system for increasing the number of messages that may be transmitted over a wired carrier channel.

One of the objects of my invention is to pro vide means for modulating two messages on a wired carrier for simultaneous reception Another object of this invention is to provide means for communicating between distant points by telephone and coded messages simultaneously over a single carrier channel.

Another object of my invention is to provide in a wired communication system carrier channels for transmitting messages of relative wide no quency bands, such as amplitude and frequency modulated radio programs, and for utilizing these same channels for transmitting two messages simultaneously of relative narrow frequency band.

Another object of my invention is to provide means for decreasing the number of transmission channels required between two points whereby the terminal apparatus and the intermediate repeater apparatus may be reduced.

Another object of my invention is to provide synchronizing or control signals from a master generator over wired carrier channels or trunk lines to the various ofilces throughout the system, whereby the multiplex mechanisms in these oflices are maintained in synchronism.

Several messages may be transmitted simultaneously over a wired trunk line by providing a different carrier wave for each message, several audible frequencies may also be transmitted simultaneously on a single carrier, and two different messages may be transmitted over a low potential or direct current trunk line by reducing the period of time for equal portions of diiierent messages and transmitting these portions in rotation. In the instant invention I separate the signals for two messages into small portions or fragments and reduce the period of time for each portion-approximately one half and then modulate the signals on a single carrier in rotation for simultaneous reception, the multiplex mechanism in each office being controlled by synchronizing signals developed by a master generator and transmitted to all the ofiices in the system.

Other objects will be'apparent from the following description taken in connection with the Figure 2 shows atrunk line provided with terminal equipment for one or two party one way carrier channel, and also terminal equipment for a one or two party two way carrier channel Figures 3 and 4 show operators cord circuits.

In Figure 1 the central offices 1 and 2, connected by the trunk line 3, may be located indifferent cities, and similar trunking arrangements may be utilized to extend wire channels to other cities. The trunk line 3 may be arranged for several carrier channels having wide frequency separation, such as a two-way two channel carrier having at one terminal a pair of jacks 4 and 5, and associated line and cut off relays 6 and l, modulating and demodulating equipment 3 for transmitting and receiving sound or control signals, the other terminal of the trunk line being equipped in a similar manner with a pair of jacks 9 and I and associated line and cut ofi relays It and I2, modulating and demodulating apparatus l3 for transmitting and receiving sound or control signals for two simultaneous messages. Cord circuits [4 and [5 comprising mechanism for grouping signals in spaced periods of time and for expandingreceived signals, may be used to connect subscriber's lines I6 and H to jacks 4 and 9 of the trunk line 3. Other cord circuits similar to M and I5 may be used to connect two other telephone subscribers lines not shown or two printing telegraph lines is and is or relay control lines and 2| may be connected to jacks 5 and In to transmit two simultaneous messages. The generators 22 are arranged to develop two diflerent low tone frequencies for controlling the relays in line 2| individually or both to ether.

A one way channel may also belprovided over the trunk line 3 primarily for transmitting signals for radio programs of either amplitude or frequency modulation, which may require a band width for frequencies up to eight thousand cycles for amplitude modulation and up to sixteen thousand cycles for frequency modulation. Therefore, this channel may be utilized for two telephone messages having frequencies around three thousand cycles each or for signals from two telegraph printers.

The equipment at one terminal of the one way channel may comprise a pair of jacks 23 and 24, relay apparatus 25 and 26, and modulating equipment 21; equipment may be provided for the opposite terminal in office .2 comprising a pair of jacks 28 and 29, line and cut on relay apparatus 30 and 3| and selecting and demodulating equipment'32. When using this channel for radio pro grams the switches 33 and 3:5 may be operated to the off position disconnecting the jacks 2 3 and 29 and associated relays from the trunk line 3. Cord circuit and 36, similar to cord circuits well known in the art, may be employed to connect the radio transmitting station over lines 3! and 38 to the trunk line 3. Cord circuits I4 and it: may be employed when it is desired to connect more than one line such as l6, l8 and 20 to the trunk line to transmit two messages at the same time.

For controlling the grouping and expanding mechanism in the several telephone offices in synchronism a master generator 39 may be employed to produce an alternating current of sine wave form preferably of ten to twenty cycles which may be transmitted over separate carriers to the distant offices in the system. Alternating current produced at 39 may be modulated on a carrier through the action of the modulation amplifier 40 and the oscillator 4|. These signals may be demodulated at 42 and applied to the square wave amplifier 43 where they are amplified and clipped in a well known manner to produce equally spaced square top positive pulses to control the grouping and expanding mechanism in the cord circuits to be more fully explained later. The signals from the generator 39 are also applied to the square wave generator 44 and the output from this amplifier of spaced positive pulses may be utilized for controlling the grouping and expanding mechanism in the cord circuits for ofiice I.

It is to be understood that the trunk line '3 may be employed to transmit signals modulated on a carrier by transmitting the carrier or suppressing the carrier, also single side band transmission may be employed. This system may be employed on power lines, telephone trunk lines, and coaxial cable.

It is to be further understood that many other channels of carrier current may be operated over the trunk line 3.

Figure 2 shows in more detail the associated terminal equipment for the multiple channel trunk line 3. The line and cut off relays 6, 1, H and I2 are associated with two channels, one channel comprising the modulation amplifier 45 and the demodulator 46 for transmitting one or two messages west to east and another channel havin a carrier current of a different frequency and comprising the modulation amplifier 41 and the demodulator 48 are for transmitting one or two messages east to west.

The line and cut off relays 25, 26, 39 and 3| are associated with one one way channel comprising the modulation amplifier 63 and demodulator 61 for transmitting radio program signals in one direction. Other channels may be employed on the same trunk line to transmit other telephone or telegraph messages.

The cord circuit in Figure 3 employs wire recording mechanism and associated circuits for grouping signals received over a subscribers line in spaced periods of time and for expanding the signals received over a connected trunk line. Two of these cord circuits may connect two subscribers lines to a single trunk line or path for the transmission over a carrier channel equal portions of two messages in successive rotation or each message may be transmitted intermittently. These cord circuits may be similar to the cord circuit shown and described in my prior application Serial Number 552,475, filed February 15, 1944, now Patent No. 2,439,701, granted April 13, 1948.

The cord circuit in Figure 4 may be similar to any conventional type cord circuit and may be employed to connect a single subscribers line with the trunk or a single transmission path.

Referring to Figure 2, sound or control signals passing over conductors 5| from west to east are applied to the hybrid coil 52 of conventional type for converting from a four wire to a two wire circuit where they are transferred to the modulation amplifier 45 and modulated on a high frequency carrier produced by the oscillator 53. The filter 54 may be employed to remove the undesired products of modulation to preferably transmit only a single side band over the trunk line 3. At the opposite or east terminal the signals are applied to the selector 56 for filtering out all undesired frequencies; from the selector 56 the signals are detected or demodulated at 46 and applied to the hybrid coil 51 to be transferred to conductors 58. Sound or control signals directed from east to west may be applied from conductors 58 to the hybrid coil 51 where they are transferred to the modulation amplifier 41 and modulated on another high frequency produced by the oscillator 59, from the amplifier 41 the signals may pass through the filter 69 to eliminate all frequencies except a single side band for transmitting over the trunk line 3 through a different channel or path. At the West terminal the signals may be applied to the selector Bl where all frequencies are blocked except the desired signals. At 48 the signals are detected and applied to the hybrid coil 52 where they may be transferred to the conductors 5|.

From the above description it has been shown that message signals may be directed from west to east over one channel and a different channel or path is employed for the return signals from east to west.

For the transmission of radio programs I have shown a one way channel. Sound or control signals from the conductors 62 may be applied to the modulation amplifier 63 and modulated on a high frequency carrier produced by the oscillator 64. The filter 65 may suppress the carrier for single side band transmission. From the filter the signals will pass over the trunk line 3 to the distant office where they will be selected by 66 and applied to the demodulation amplifier 61. After detection the signals are supplied to the conductors 68.

It is to be understood that a carrier and one side band may also be employed rather than single side band transmission.

With further reference to Figure 2, the conductors 5| and 58 terminate in a pair of jacks in parallel for connecting two cord circuits to the same carrier channels for the transmission and reception of two different messages simultaneously. Jacks 4 and 9 may be known as the A party jacks and the jacks 5 and I0 may be known as the B party jacks. Associated with each jack are line and cut off relays. The line relay or drop signal 6 Sassociated with the A party jack at the west terminal is adapted to be actuated by alternating current supplied from a cord circuit connected to the A party jack '9 at the east terminal, and the cut off relay 10 associated with jack 4 is energized over the sleeve conductor of jack 4 from battery in the connecting cord circuit. Adapted to be operated in like manner are the line'relays H, 12 and 13 and the cut off relays 14-, 15 and 16 associated with the jacks 5, 9 and I0 respectively. The cut off relays I4 and I6 associated with the B. party jacks are adapted to be energized through resistors 11 and iii to affect certain changes in the connecting cord circuit to be explained later. The energization of any line relay 69, II, 12 or 13 will cause its associated signal lamp I9, 86, 8I or 82 to glow notifying the operator that a connection is desired. Spaced pulses from the square wave amplifier 99 are applied to the signal control relay 99 to alternately energize and deenergize the relay during equal periods of time. The relay 83 in its deenergized position maintains a closed circuit through the line relay '69 at contacts 84 and holds the circuit through the line relay II open at contacts 85. The relay 83 upon energizing holds the circuit of relay 69 open at contacts 89 and closes the circuit for relay II at contacts 93 so that the line relays 69 and II are alternately placed in condition to be actuated by ringing current over the carrier channel for equal periods of time. Therefore, the relays-69 and II may be actuated by ringing current from the cord circuits connected to jacks 9 and I9 to be more fully explained later.

The relay 86 at the east terminal willbe energized and deener-gized from spaced pulses supplied irom the square wave amplifier 43 to open and close the circuits through the line relays 12 and '39 at contacts 91 and 88 during equal periods of time. Therefore, the relays I2 and I3 may be actuated by signal current supplied through jacks i and 5. The relays 93 and 86 will be energized and deenergized in synchronism since all control pulses are supplied by one master generator 39 as explained in connection with Figure 1. Similar terminal apparatus and circuits may be employed for other carrier channels.

From the above description it has been shown that an operator may be signalled in either direction for the A or B party over the carrier current channels.

Should it be desired to employ the carrier channels for only one message rather than two simultaneous messages, then dummy plugs may be inserted in the B party jacks 5 and I6 and the switches 99 and 99 operated to open the circuit for relays ii and i3, and to maintain the line relays 99 and I2 across the conductors 5| and 58 without being interrupted by the action of relays 99 and 86.

The conductors 62 and 68 for the one way radio program channel terminates in a pair of jacks in parallel for connecting two cord circuits to the same channel for the transmission of two different messages simultaneously when not in use for radio programs. Jacks 23 and 28 may be known as the A party jacks and jacks 24 and-29 may be known as the B party jacks. Associated with jacks 23 and 24 are relays 25 and 26 connected to the sleeve conductor of the jacks to produce certain effects in the connecting cord circuits to be explained later. Relay 26 is adapted to be energized through a resistor 9I-. Associated with jacks 29 and 29 are line and cut off relays. The line relays or drop signals 92 and 93 associated with the jacks 28 and 29 are adapted to be operated by alternating current supplied from cord circuits connected to the jacks 23 and 24 respectively, and the cut off relays 94 and 95 associated with jacks 28 and 29 are energized over the sleeve conductors of these jacks from battery in the connecting cord circuits. The cut off relay 95 is adapted to be energized through resistor 99 to affect certain changes in the cord circuit. The energization of line'relays 92 or 93.

will cause its associated signal lamp 91 or 98 to glow notifying the operator that a connection is desired. Spaced pulses from the square wave amplifier 43 are applied to the signal control relay 99 to alternately energize and deenergize this relay during equal periods of time. The relay 99 in its deenergized position maintains a closed circuit through the line relay 92 at contacts I66 and holds the circuit through relay 93 open at contacts I9I, so that the line relays 92 and 93 are alternately placed in condition to be actuatedby ringing current over the carrier channel during equal periods of time. Therefore, the relays 92 and 93 may be separately actuated by ringing current from the cord circuits connected to jacks 23 and 29.

The relay 99 will be energized and deenergized from spaced pulses supplied from the square wave amplifier 43 to open and close the circuits through the line relays 92 and 93 at contacts I96 and II during equal periods of time. i

From the above description it has been shown that an operator may be signalled from either the A or B party jack over a one way carrier current channel. i

When it is desired to employ the one way channel for radio program transmission the keys 33 and 39 would be operated disconnecting the B party jacks and associated equipment from the channel conductors 62 and 68 and maintaining the circuit of relay 92 across conductors 68without being interrupted through the action of relay 99.

With reference to Figure 3, which shows a cord circuit for connecting a telephone line, or a printing telegraph line, or a relay signalling line to a multi-party carrier channel of Figure 2 as illustrated in Figure 1 at It and I5. The cord circuit includes recording and reproducing mechanism for grouping and separating sound signals so that two cord circuits may be employed at each terminal of the trunk or carrier channel for transmitting two separate and private messages over a carrier trunk at the same time.

The plug I92 is a calling or answering plug for the subscribers lines, and the plug I63 is a calling or answering plug for the trunk line or carrier channel. Battery at I94 is fed to the telephone or other subscriber lines through the resistance I95, secondary winding of transformer I66, winding I91 of anti-sidetone transformer 98. The operator may ring on the telephone line through the action of key I99, and she may talk to the telephone subscriber by operating the key H9. The usual disconnect signal is provided at I I I, which is caused to glow by the relay II2 returning to normal position when the subscriber on the connected line hangs up his receiver. Key I99 would not be operated when the cord is connected to a printing telegraph or relay signalling line. Battery at H3 is fed through resistor II4, conductors H5 and H6 when certain relays in the cord circuit are operated, to be explained later. secondary winding of transformer III, winding I I8 of the anti-tone transformer Il9, tip of plug I93, conductors 5f or 58 in Figure '2,

through a four wire two wire hybrid coil 52 or,

51, ring of jack I63 to opposite side of battery. A disconnect signal is provided at I29 which may be actuated by the relay I2 I.

69 from the conductors 5i. Relays I22 and I23 sava es 7 upon energizing completes a circuit from the square wave amplifier 44, conductor I24, springs I25, springs I26 and I2! to relay I28; Therefore relay I 28- is energized and deenergized during equal periods of time by the spaced pulses from the amplifier 44. Relay I28 in its normal or aleenergized position shorts the very high resistance I29 over conductor II5, springs I30, springs I 3I, conductor H6. The duration of this condition may be considered one talking period for the A party. Ringing current may be sent out over the channel by operating the key I32 during. the A party interval throughsprings I33 and I34 to operate the relay 12. Should the plug I03 be connected to the B jack ringing current maybe supplied to the conductors 5I' during the B party interval through the contacts I35 to operate relay I3. Relay I28 during the period that itis energized opens the contact springs I to include the resistance I29 in the battery circuit feeding the tip and ring conductors, thereby rendering the cord circuit inoperative or blocked to sound signals, which may be known as the B party talk ing period. Since the control signals are in synchronism relays 83, 86 and I 28 will be operated in unison, and line relay I2- will be cleared from the line during the B party talking period In order that two messages may be transmitted over a single channel, I reduce the interval of portions" or fragments of each message by approximately one half and transmit these grouped portions-in alternate periods of time. Therefore, by recording the signals from the subscribers line or the operators telephone set on a magnetio wire or tape and reproducing the signals by a coil traveling in the opposite direction to that of the wire and at approximately the same speed, the-interval for each portion will be reduced and the frequency of the signals will be increased;

The sound signals from a connected telephone line or the variable signals from a printing telegraph or low tone subscribers line would pass through the cord tip conductor, winding I 01, and the alternating current component seeking the path of least impedance would pass through windings I36 and I3! of the transformer I08, condenser I38 to ring conductor. The primary winding of audio transformer I39 bridged across the winding I of transformer I08 will vary the potential on the grid I40 of the amplifier tube MI in* accordance with signals received over the subscribers line. The anode output of tube I4I' may be applied through the transformer I42 to" the stationary recording coil I43 for recording the signals magnetically on the moving wire or tape I44.

In the recording and reproducing mechanism I preferably employ an endless wire I44 of small diameter traveling in the direction indicated by the arrows over the pulleys I45, I46, I 41, I48, I49 and I50. The pulley I48 is driven at a uniform speed by a motor I52 through the friction clutch indicated by the dashed circle I53; Attached to the pulley I48 is a disk of larger diameter I5 4", driving the member I55 on the slide bars I56 and IS! in a reciprocating motion through the action of the connected arm I58 attached near the rim of the disk I54 so that the distance traveled right tol'eft by the member I 55 is approximately equal to the distance traveled by the wire in one half revolution of the pulley and disks I48 and I54".

The signals recorded on the wire I44 by the coil 143 may be picked up by the reproducing coil I59 traveling from right to left or in a direcnon reverseto' that of the wire" so that theslg= rials will be reproduced in the coil I 50 in one half or the intervalthat was required to record them on the wire. The coil I59 traveling from left to right moves very nearly at the same speed and in the same direction as the Wire. Therefore the coil I59 would be inactive and as will be shown later the signals would be blocked in the cord circuit during the left to right movement of the coil;

The signals reproduced by the coil I59 are applied to the grid I60 of the amplifier tube I6I. The output of tube I6I is applied to the primary winding of transformer II! to vary the current supplied by battery II3 to the trunk line over a path as previously described. Therefore, it has been shown that the sound signals from the subseriber's line may be separated into small portions; and rouped by the interval being reduced through the reciprocating action of the coil I59, and then transmitted over the carrier channel in spaced: periods of time. As shown in Figure 1 another cord circuit I5" may be employed in offioe- 2 to connect a telephone line or printing telegraph line with the A jack 9 of the trunk line. This cord circuit as previously stated may be exactly like the cord circuit of Figure 3. Therefore; signals originating in ofiice 2 and transmitted over the'trunk line would also be in spaced groups and the alternating current component would flow through windings H8, I52 and E33 of the anti-sidetone transformer I I9, condenser I54 to the opposite side of the line. The primary winding of transformer I65 bridged across the winding I52 will cause the potential on the grid I68 of amplifier I67 to vary in accordance with the'sou'nd signals received from the carrier channel. The anode output of tube I6? is applied through the audio transformer I63 to the recording coil I69 mounted on the member I55 and traveling forward and backward along the wire I44 to record sound signals thereon during the right to left movement of the coil only. The coil'travels left to right in the same direction and approximately the same speed as the wire, therefore no signals would be developed. Furthermore the cordcircuit will be blocked during this period by including the resistor I29 in the battery supply circuit. The coil I59 in moving right to left along the wire I44 in a direction opposite to the movement of the wire will cause the signals who recorded over a length of the wire I44 equal to approximately twice the distance that the coil I69 travels right to left, so that the signals received over the trunk line will be expanded to" their normal interval and reproduced in the stationary coil I 10 and applied to the grid I'II of the amplifier tube H2. The anode output of tube I12 may be applied to the primary winding of the transformer I06 to vary the current in the telephone line over a path as previously described.

The coils I13 and I14 are high frequency erasing= coils for restoring or demagnetizin the wire I44 so that further messages may be recorded thereon.

The pole pieces for the recording and reproducing coils are provided with a narrow slot for the wire I44 to travel through.

The A party talking periods over the carrier channel or trunk line are the periods between synchronizing pulses, and the B party talking periods are during the intervals of the synchronizing. pulses, which are the same in each two party channel or path throughout the system. motherwordasigziaisoriginating in oflice I and 9 transmitted over A party trunk would be transmitted during the intervals between control pulses and the answer from a subscriber in office 2 would also be transmitted during the intervals between control pulses.

In order to synchronize the grouping and separating mechanism with the proper party A or B on the trunk line, I provide holding or retarding magnets I15 and I16 for holding the disk I54 so that the member I55 will be held or retarded until a control pulse is received. The magnet I15 may be considered the A party holding magnet and in its nonoperated position as shown in the drawing it holds the disk I54 from rotating by the armature bar I'I'I engaging the pin I18 in the disk I54. As soon as a control pulse is received over conductor I21, the magnet I15 is energized in parallel with relay I28 through springs I25, I25 and I21, and conductor I19, during the intervals of the control pulses to permit the disk I54 to rotate. The motor is arranged to drive the disk a little faster than one revolution per cycle of the control signals so that the bar II! will slightly retard the disk just before the control pulse is received. The magnet H6 is continuously energized while the plug I06 is connected to the A party jack through the springs I88, I8I and I82 and the conductor I83, to hold its armature bar I84 out of engagement with pin I85.

From the above it has been shown that the member I55 will move from right to left while the relay I28 is deenergized to transmit sound signals during the intervals between control pulses, and that during the intervals of the control signals the cord circuit is blocked by including the resistance I29 in the talking path. As previously explained another cord circuit similar to Figure 3 will be employed in office 2 so that a subscriber in office I and a subscriber in oifice 2 may talk over the A party channel or trunk line. A second subscriber in office I may talk to a second subscriber in office 2 at the same time over the B party channel or path. In which case another cord circuit similar to Figure 3 would be connected to the B jack in oflice I, and a similar cord circuit would be connected to the B jack III in office 2.

Inserting the plug I03 into the 38 Jack 5 will cause relays I I and I23 to be energized through the resistance 'I'I over the sleeve conductors, relay IE2 is arranged so that its armature Will not be operated when the resistor 17 is included in its energizing circuit. Therefore relay I85 will be energized intermittently by the control signals over conductor I24, and through the springs I25, We and I8? to the relay I86. Relay I85 during its energized position may be considered the B party talking period and the resistor I29 is shortened at spring I88 during the intervals of the control pulses, and in the intervals between pulses the resistor I29 is included in the talking path to block the signals and to reduce the current drain. Instead of using the resistor I29 the talking path could be opened and closed by the relay I55. The holding magnet Ilfi will be operated in unison with the relay I86 over conductor I85 and springs I25 and I25, to retard the rotation of the disk I 58 by the armature arm tilt engaging the pin I85, which places the member I55 in position to start moving to the left at the instant a control signal is received. Holding magnet H5 is held in its operated position when the cord is used with B party trunk lines, over conductor I'I'9 through springs I89, I8I and I88 to ground. The remainder of the apparatus and associated cir- 10 cuits in the cord functions as described in connection with the A party.

From the above it has been shown that two private messages may be transmitted over a single channel by grouping the signals in alternate spaced periods, and also that the operator may be signalled in either direction. It is also shown that the cord circuit of Figure 3 may be-used for either A or B connections.

The cord circuit of Figure 3 may be used with the one way channel circuit in the same manner as described above for the two channel two way circuit except that signals would only be transmitted from west to east. Also the operator would only be signalled in one direction. The operation of ringing key I32 would cause ringing current to be sent out over the carrier channel during a period depending upon which party jack is used. Should plug I03 be inserted in the A party jack then ringing current will only be supplied to the carrier channel during the A party intervals through springs I33 and I34, and when the plug I93 is connected to a B jack ringing current will only be supplied to the channel during the B p rty interval through the contacts I 35. I

The message signals in the trunk line are in spaced intervals, but after passing through the cord circuit they are again connected together in a continuous message, Hence the telegraph and relay tone signals in the called line will be like the original signals in the calling line.

When it is desired to use the one way channel circuits or the two way double channel circuits for only one message at a time rather than two simultaneous messages the keys 33 and 34 would be operated to disassociate the B party apparatus from the trunk line, and the switches 89 and 99 would be operated to disconnect the B party line relay from the trunk line, and the cord circuit of Figure 4 would be used as illustrated at 35 and 3B, Figure 1.

Figure 4 shows a conventional cord circuit provided with a pair of plugs I93 and I94, ringing keys I95 and I96, listening key I91 and a, signal lamp to indicate subscribers disconnect. This cord circuit to be used when it is desired to connect a radio transmitting station or any time it is desired to transmit a message having a very wide frequency band.

In the various circuits shown and described I have simplified the drawings by indicating the source of potential by a positive or negative sign. Also I have omitted the heater elements from the various tubes.

The embodiments of the invention which have been given herein are illustrations of how the various features may be accomplished and of the principles involved. It is to be understood that the invention contained herein is capable of embodiments in other forms and adaptations, without departing from the spirit of the invention and the scope of the appended claims.

I claim:

1. In a telephone system, a trunk line provided at one terminal with a pair of jacks and a relay for each jack, an oscillator for producing a carrier current channel for said trunk line, means foractuating either one of said relays independently over said channel, and switching means for disconnecting one of said jacks and its associated relay from said trunk line.

2. In a telephone system, first and second telephone ofiices, a trunk line extending between said Ofi'lCBS adapted for simultaneous transmission of a number'of carrier waves, a pair of jacks associated with each terminal of said line for each of the said carrier waves, a signal associated with each of the said jacks for informing an operator that a connectionis desired, a link circuit adapted to be connected to the said jacks in said first ofiice, and means in said link circuit connected to a jack in the first ofiice to intermittently supply signalling current tosaid, line tomodulate one of said carrier waves, thereby actuating a signal in said second ofiiceto indicate the jack for answering the call.

3. In a communication system, a trunk line adapted for the simultaneous transmission of a number of carrier waves, a pair of jacks associated with said line for each of the said carrier waves, a plurality of link circuits each provided with plug-in terminals for connecting with anyone of said jacks, said link circuits comprising mechanism for grouping electrical signals, and means including two of said, link circuits for transmitting signals representative of two simultaneous messages over any one of said carrier waves.

4. In a telephone system, first and second tele phone offices, a trunk line extending between said ofiices adapted for simultaneous transmission of a number of carrier waves, a. pair of jacks associated with each terminal of said line for each of the said carrier waves, a signal associatedwith each of said jacks for informing anoperator that a connection is desired, linkcircuits in each of said offices adapted to be; connected tosaid-jacks, each of said link circuits-comprising mechanism for grouping electrical signals, means in said link circuit connected to a jackin the first oifice for actuating a signal in said second oifice to indicate the jack for connecting anotherlink circuit to answer the call, means, following the connection of the second link circuitfortransmitting signals representative of a telephone message from the first office to the second ofiice over one of said carrier waves in, spaced periods of time, a generator at said first oflice for producing control signals, means for transmitting said control signals to saidsecond offline, and means at said oifices responsive to said signals. for controlling the grouping mechanism in both, ofiices. in synchronism.

5. In a telephone system, first and: second telephone offices, a trunk line extending from the first ofiice to the second oflice, means at the first ofiice to produce a carrier wave means to transmit said carrier wave over said; trunk line, a first pair of subscribers lines at said first oflice, a first pair of cord circuits for interconnecting said subscribers lines to said trunk line, means in said cord circuits to select different portions of the signals representative of two telephone messages received from said pair of lines, means to modulate the selected signals for both, messages in rotation on said carrier wave, a second. pair of, lines at said second oflice, a second pair of cord circuits for interconnecting said second pair of lines to said trunk line, and meansin said second pair of cord circuits to select the signals received over said carrier wave to transmit separate telephone messages over each line of said second pair of lines.

6. In a communication system, a trunk line, means to receive from said trunk line different sets of control signaIs means to receive from said trunk line control impulses, a first line and a second line each provided with a relay, a pair of cord circuits for connecting said first and said second lines to said trunk line, means in, one of said cord circuits under control of said impulses to. select a first set of said control signals to transmit the selected signals over said first line to control its associated relay, and means in another one of said cord circuits under control of said impulses to select a second set of said control signals to transmit the second set of signals over said second line to control its associated relay.

7. In a telephone system, a trunk line, means to produce a number of carrier waves, means to transmit said carrier waves over said trunk line, a pair of jacks associated with said trunk line for each of the said carrier waves, a plurality of link circuits each provided with plug-in terminals for connecting with any one of said jacks, each of the said link circuits comprising means to select dilTe-rent portions of electrical signals, representative of a telephone message, and means including two of said link circuits to modulate signals for two telephone messages on any one of said carrier Waves in recurring intervals.

8. In a telephone system, a subscribers line, a trunk line provided with means for generating a carrier wave, a cord circuit for connecting said subscribers line to said trunk line, a generator to produce control waves, an amplifier, means including said amplifier to produce spaced control impulses from said control waves, and means in said cord circuit under control of said impulses for separating sound signals received from said subscribers line into equal portions, and for reducing the interval of each portion to modulate said carrier wave during spaced periods of time,

, said last means comprising devices for recording said signals on a movable telegraphone wire and movable devices adapted to travel in a, direction opposite to said wire for reproducing said signals in space periods.

9. In a communication system, a line, a trunk line provided with means for developing a carrier wave, a cord circuit for connecting said first line to said trunk line, means to produce control waves, an amplifier, means including said amplifier to produce spaced control impulses from said control waves, and means in said cord circuit under control of said impulses to group signals re-- ceived from said first line into spaced portions to modulate said carrier wave during spaced periods of time, said last means comprising devices 'for recording said signals on a movable telegraphcne wire and movable devices adapted to travel in a direction opposite to said wire for reproducing said signals in groups.

10. In a communication system for the trans mission of at least two sets of control signals, a trunk line terminating into a first branch line and a second branch line, means for producing a carrier wave, means including said carrier wave for transmitting said control signals in like manner over said trunk line, a generator to produce control waves, an amplifier, means including said amplifier to produce spaced synchronizing impulses from said control waves, means to produce a second carrier wave, means including said second carrier wave to transmit said control waves over said trunk line, means comprising apparatus and suitable circuits under control of said synchronizing impulses to select one of said sets of control signals to. transmit the selected control signals over said first branch line, and means comprising otherapparatus and associated circuits under control of said synchronizing impulses to select a second one of said sets of con- 13 trol signals to transmit the second set of control signals over said second branch line.

11. In a telephone system, a first and a second telephone office, a trunk line extending from said first ofiice to said second office for transmitting signals modulated on a carrier wave, signal se lecting means in said first ofiice including a first movable member to select portions of said signals corresponding to two telephone messages to modulate said carrier wave with the selected portions of said signals for each message in a different recurrent period of time, means in the second oflice including a second movable member for separating the selected portions of said signals received over said trunk line, a generator at said first office to produce control signals, means to transmit the said control signals to said second oflice, means at said first oifice including a first electric device responsive to said control signals for controlling said selecting means, and signal separating means at said second office including a second electric device responsive to said received control signals for controlling said separating means.

12. In a telephone system, a trunk line provided at one terminal with a pair of jacks, and a relay for each jack at the opposite terminal, an oscillator to produce a carrier wave, means to transmit said carrier wave over said trunk line, a cord circuit havin a plug for detachabiy connecting the said cord circuit through either one of said jacks to said trunk line, and means in said cord circuit to intermittently supply signaling current to said trunk line to modulate said carrier wave during different recurring periods depending upon the jack connected with the cord circuit to actuate the said relay associated with the connected jack.

13. In a telephone system, a trunk line, means to produce a carrier Wave, means to transmit said carrier wave Over said trunk line, a pair of subscribers lines, a pair of cord circuits for interconnecting said subscriber's lines to said trunk line, and means including a movable member in each of the said cord circuits to modulate said carrier wave with portions of the message signals transmitted simultaneously over said pair of lines in a different recurrent period for each message.

14. In a telephone system, a trunk line extending from a first ofiice to a second ofiice, means in the first office to produce a carrier wave, means to transmit said carrier wave over said trunk line, means in the first office to produce control waves, amplifier means responsive to said control waves to produce spaced control signals, means to transmit said control waves to the second office, a plurality of relays in the second ofiice associated with said trunk line, amplifier means in the second ofiice responsive to received control Waves to produce spaced synchronizing signals, electro-magnetic means in the second oflice under control of said synchronizing signals to connect the said relays in successive rotation to said trunk line, and electro-magnetic means in the first ofiice under control of said control signals to cause ringing current to be modulated on said carrier wave during a certain recurrent period to energize one of said relays,

JOHN H. HOMRIGHOUS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS- Number Name Date 1,548,260 Espenshied Aug. 4, 1925 1,624,596 Hartley Apr. 12, 1927 2,031,696 Espenchied et a1. Feb. 25, 1936 2,094,132 Miller Sept. 28, 1937 2,105,016 H. H. Smith Jan. 11, 1938 2,170,751 Gabrilovitch Aug. 22, 1939 2,263,369 Skillman Nov. 18, 1941 2,271,721 J. E. Smith Feb. 3, 1942 2,278,788 Knick Apr. 7, 1942 2,289,048 Sandalls July 7, 1942 2,387,018 Hartley Oct. 16, 1945 2,395,467 Deloraine Feb. 26, 1946 2,430,471 Lang Nov. 11, 1947 2,434,697 C. H. Homrighous Jan. 20, 1948 2,434,698 J. H. Homrighous Jan. 20, 1948 

